Projection type screen and image projection system

ABSTRACT

A projection type screen comprises a reflection surface array and a lenticular sheet. In the reflection surface array, a plurality of reflection surfaces is located along a horizontal direction. Each reflection surface has a mirror reflectivity of which section along the horizontal direction is quadratic curve shape. The lenticular sheet is located at an incident side of a projection light for the reflection surface array. The lenticular sheet has diffusivity along a vertical direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2005-81984, filed on Mar. 22,2005; the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a projection type screen and imageprojection system for a user to perform autostereoscopy.

BACKGROUND OF THE INVENTION

A stereoscopic image display apparatus capable of autostereoscopy is asan apparatus for displaying a stereoscopic image, for example, without aspecial device such as a polarized glass or a glass with shutter.

For example, in Japanese Patent No. 3323575 (pp 3, FIG. 1) . . .(reference 1), a plurality of images, each having a different viewposition, are respectively projected by a plurality of projectors fromthe back of a transmission type screen. By observing the transmissionlight through a lenticular lens located in front of the screen, a usercan observe a stereoscopic image.

Furthermore, in Japanese Patent Disclosure (Kokai) PH9-0189884 (pp 4,FIG. 1) . . . (reference 2), on a projection type screen in which aplurality of rotatable reflection mirrors are arranged along ahorizontal direction, a plurality of images each having different viewposition are projected by switching in time. In this case, the user canalso observe a stereoscopic image.

Furthermore, in “H. Kaneko, T. Ohshima, O. Ebina and A. Arimoto,“Desktop Autostereoscopic Display Using Compact LED Projectors and CDRScreen”, SID 02 DIGEST, pp. 1418-1421, 2002” . . . (reference 3), aplurality of projectors projects an image onto a projection type screenhaving shape of corner reflection mirror. By observing the reflectionlight at a position of the projector, the user can also observe thestereoscopic image.

In order to widely use the stereoscopic display apparatus, theobservable area of a stereoscopic image should be wide, and a scale ofapparatus necessary to display the stereoscopic image should not belarge. Especially, a small number of projectors necessary to display thestereoscopic image is important to prevent the scale of apparatus frombeing large. Without special function, it is desired that thestereoscopic image is displayed by one projector.

However, in the stereoscopic image display apparatus of the references 1and 3, a plurality of projectors is necessary. Especially, in order tosimultaneously observe a stereoscopic image from a plurality of viewpositions by extending an observable area, the number of projectors hasto be increased. In this case, a scale of the apparatus becomes large.

Furthermore, in the stereoscopic image display apparatus of thereference 2, in synchronization with a projection image timely switchedby a projector, rotation of reflection mirrors set on a screen has to becontrolled. Accordingly, in the projector outgoing the image, acontroller to synchronize rotation of the projection image with thereflection mirrors is necessary. In case of using this method, a usualprojector cannot display the stereoscopic image.

SUMMARY OF THE INVENTION

The present invention is directed to a projection type screen and imageprojection system for a user able to observe by autostereoscopy using ausual projector.

According to an aspect of the present invention, there is provided aprojection type screen comprising: a reflection surface array in which aplurality of reflection surfaces are located along a horizontaldirection, each reflection surface having a mirror reflectivity of whichsection along the horizontal direction is quadratic curve shape; and alenticular sheet located at an incident side of a projection light forthe reflection surface array, the lenticular sheet having diffusivityalong a vertical direction.

According to another aspect of the present invention, there is alsoprovided an image projection system comprising: a light emittingapparatus emitting a projection light including a display image; and aprojection type screen on which the projection light is incident;wherein said projection type screen comprises a reflection surface arrayin which a plurality of reflection surfaces are located along ahorizontal direction, each reflection surface having a mirrorreflectivity of which section along the horizontal direction isquadratic curve shape; and a lenticular sheet located at an incidentside of a projection light for the reflection surface array, thelenticular sheet having diffusivity along a vertical direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows components of an image projection system including aprojection type screen according to a first embodiment of the presentinvention.

FIGS. 2A and 2B are sectional views of the projection type screen alonga horizontal direction according to the first embodiment.

FIG. 3 is a sectional view of the projection type screen along avertical direction according to the first embodiment.

FIG. 4 is a schematic diagram showing function of a stereoscopic displayapparatus of direct view type.

FIG. 5 shows one example of a display image of the stereoscopic displayapparatus of direct view type.

FIG. 6 is a schematic diagram of function of the projection type screenaccording to the first embodiment.

FIG. 7 is a schematic diagram showing a relationship between aprojection light and a reflection surface array of the projection typescreen according to the first embodiment.

FIG. 8 is a schematic diagram showing a relationship between aprojection light and a pitch of the reflection surface array in theprojection type screen according to the first embodiment.

FIGS. 9A and 9B are schematic diagrams showing a relationship betweenthe projection type screen and the stereoscopic display apparatus ofdirect view type according to the first embodiment.

FIG. 10 is a schematic diagram showing a relationship between a pitchand a focus distance of the projection type screen according to thefirst embodiment.

FIG. 11 shows reflection light of a parallel light incident onto theprojection type screen according to the first embodiment.

FIG. 12 shows reflection light of a diffusive light incident onto theprojection type screen according to the first embodiment.

FIG. 13 shows first modification example of the projection type screenaccording to the first embodiment.

FIG. 14 shows second modification example of the projection type screenaccording to the first embodiment.

FIG. 15 shows third modification example of the projection type screenaccording to the first embodiment.

FIGS. 16A and 16B are schematic diagrams showing a relationship betweenthe modification of the projection type screen and the stereoscopicdisplay apparatus of direct view type according to the first embodiment.

FIG. 17 shows a fourth modification example of the projection typescreen according to the first embodiment.

FIGS. 18A and 18B show components of a projection type screen accordingto a second embodiment of the present invention.

FIG. 19 is a schematic diagram showing a relationship among eachreflection surface of the projection type screen according to the secondembodiment.

FIG. 20 is a schematic diagram showing a relationship among a pitch, aprojection distance, and a focus distance of the projection type screenaccording to the second embodiment.

FIG. 21 is a schematic diagram of a first modification of the projectiontype screen according to the second embodiment.

FIG. 22 is a schematic diagram of a second modification of theprojection type screen according to the second embodiment.

FIG. 23 is a schematic diagram of a third modification of the projectiontype screen according to the second embodiment.

FIG. 24 shows components of a projection type screen according to athird embodiment of the present invention.

FIG. 25 is a schematic diagram showing a function of elements ofselecting transmission and scattering state according to the thirdembodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, various embodiments of the present invention will beexplained by referring to the drawings. The present invention is notlimited to the following embodiments.

The First Embodiment

FIG. 1 is a block diagram of an image projection system having aprojection type screen according to a first embodiment of the presentinvention. The projection type screen 101 comprises a reflection surfacearray 102 and a lenticular sheet 103. In the reflection surface array102, a plurality of reflection surfaces each having mirror reflectivityis located along a horizontal direction. The lenticular sheet 103 hasdiffusivity along a vertical direction.

Furthermore, a projection light 1 is outgoing from a projector 201 as alight emitting apparatus to the projection type screen 101. An observerviews a reflection light 2 of the projection light 1. In FIG. 1, thenumber of reflection surfaces in the reflection surface array 102 iseight. Actually, several hundred reflection surfaces may be used basedon the display resolution of a stereoscopic image. As the projector 201,for example, a DLP (Digital Light Processing) projector using DMD(Digital micro Mirror Device) and a liquid crystal projector using aliquid crystal display device are used. Furthermore, an opticalmodulation device using a diffraction grating, for example, a projectorof laser scanning type, can be used.

FIGS. 2 and 3 are respectively sections along a horizontal direction anda vertical direction of the projection type screen according to thefirst embodiment.

As shown in FIG. 2A, a section of each reflection surface of thereflection surface array 102 along a horizontal direction is a concavequadratic curve facing an incident direction of the projection light 1.In this case, the quadratic curve has a parabolic shape. As shown inFIG. 2B, a directrix of a parabola of each reflection surface coincides,and a focus point of the parabola of each reflection surface exists onthe same straight line parallel to the directrix.

On the other hand, as shown in FIG. 3, a section of the lenticular sheet103 along a vertical direction is convex to the incident light 1.Accordingly, the lenticular sheet 103 diffuses the incident light 1along a vertical direction. In this case, diffusion degree of thereflection light 2 is determined by a lens parameter such as a focusdistance calculated by a lens shape of the lenticular sheet 103. Thelenticular sheet 103 diffuses the reflection light 2 reflected by thereflection surface array 102 along a vertical direction. Accordingly, anincident position of the projection light 1 on the lenticular sheet 103may not be strictly determined.

Next, a principle to display a stereoscopic image by the projection typescreen 101 is explained. First, a principle of autostereoscopy in astereoscopic image display apparatus of direct view type is explained.FIG. 4 shows a section along a horizontal direction in the stereoscopicimage display apparatus to observe three images (A, B and C) fromdifferent eye positions. In the stereoscopic image display apparatus ofFIG. 4, as shown in FIG. 5, images A, B and C are divided as a stripshape along a vertical direction and are display-arranged in order. Abarrier 302 as a slit is located in front of a display 301. As shown inFIG. 4, by setting the barrier 302 in front of the display 301, eachimage can be observed from a predetermined direction. By adjusting apitch to display each image on the display 301 and a space of slit ofthe barrier 302, a direction from which each image is observable is setas angle narrower than both eyes of the observer. In this case, theobserver can view the stereoscopic image. For example, in FIG. 4, if animage A and an image B are a stereo image, autostereoscopy is realizedby simultaneously observing the image A and the image B.

FIG. 6 is a schematic diagram to explain function of the projection typescreen of the first embodiment using the principle of autostereoscopy.First, projection light 1 is outgoing from the projector 201 to theprojection type screen 101. The projection light 1 includes three kindsof images A, B and C. Each image is divided as a strip shape along avertical direction and arranged in order as shown in FIG. 5.

In order for an usual projector to obtain such image, as shown in FIG.7, each image is divided as a strip shape along a vertical direction,and displayed by arranging in order on an image display device 201 a ofthe projector 201. These images are projected with magnification througha projection lens 201 b of the projector 201. In this case, an imageoutgoing from the projector 201 and projected on the projection typescreen 101 is a reverse image of the image displayed on the imagedisplay device 201 a of the projector 201. Accordingly, in order todisplay a normal image at the incident timing, the reverse image has tobe displayed on the image display device 201 a.

The projection light 1 outgoing from the projector 201 is incident ontoeach reflection surface of the reflection surface array 102. In thiscase, each reflection surface of the reflection surface array 102 has aconcave parabolic shape facing an incident direction of the projectionlight 1. Accordingly, a direction of the reflection light is differentby the incident position of the projection light 1. If the projector 201is sufficiently far from the projection screen 101, the projection light1 is incident as a parallel light onto the projection type screen 101.Accordingly, as shown in FIG. 8, a pitch between neighboring reflectionsurfaces on the reflection surface array 102 and a pitch of incidentposition of each image included in the projection light 1 on thereflection surface has to be arranged. In this case, a reflectiondirection of each image in the incident light 1 can be arranged on thereflection surface array 102, and each image can be observed fromrespective predetermined direction. In the same way as the stereoscopicimage display apparatus of FIG. 4, by setting an observable direction ofeach image at an angle narrower than a space between the eyes of anobserver, the observer can view the stereoscopic image.

FIGS. 9A and 9B are schematic diagrams showing the relationship betweenthe stereoscopic image display apparatus in FIG. 4 and the projectiontype screen of the first embodiment. Concretely, in the stereoscopicimage display apparatus of FIG. 9A, by covering a display 301 with abarrier 302 having slits, each image (A, B, C) on the display 301 can beobserved from a predetermined direction. On the other hand, in theprojection type screen 101 of FIG. 9B, each reflection surface has aparabolic shape, and incident projection light 1 is reflected alongdifferent directions according to the incident position on thereflection surface 102. Accordingly, by arranging a pitch of eachreflection surface and a pitch of each image in the projection light 1,each image (A, B, C) can be observed from a respective predetermineddirection.

Next, as for each reflection surface of the reflection surface 102 ofthe projection type screen 101, relationship between a focus distance gof the reflection surface and a pitch D between neighboring reflectionsurfaces is explained.

As shown in FIG. 10, a coordinate of a point P on a reflection surfaceis represented by polar coordinates (ρ, φ) centering a focus point ofthe reflection surface. In this case, ρ represents a distance from thefocus point to the point P on the reflection surface, and φ representsan angle between a straight line passing through the focus point andperpendicular to the directrix and a straight line passing through thefocus point and the point P. The relationship between the focus distanceg and the point P on the reflection surface is represented as followingequation (1).

$\begin{matrix}{\rho = \frac{2g}{1 + {\cos \; \varphi}}} & (1)\end{matrix}$

In this case, the maximum outgoing angle (φ in case that P is on theedge of the reflection surface) of reflection light is φ_(MAX), and ρfor the maximum outgoing angle φ_(MAX) is ρ_(MAX). The pitch D betweenreflection surfaces of the reflection surface array 102 is representedas following equation (2).

$\begin{matrix}{D = \frac{4{g \cdot \sin}\; \varphi_{MAX}}{1 + {\cos \; \varphi_{MAX}}}} & (2)\end{matrix}$

The maximum outgoing angle φ_(MAX) of reflection light is a parameter toregulate observable area of stereoscopic image. If the observable areais previously set as φ_(MAX), a pitch D of neighboring reflectionsurfaces of the reflection surface array 102 is calculated from a focusdistance g of reflection surface using the equation (2). By arranging aplurality of reflection surfaces based on the pitch D, the reflectionarray 102 of the projection type screen 101 can be obtained.

As mentioned-above, in the projection type screen, a plurality of imagesin the projection light from the projector are respectively reflectedalong different directions by the reflection surface array in whichsection of each reflection surface along a horizontal direction has aparabolic shape. In this case, by arranging a pitch between neighboringreflection surfaces and a pitch of each divided image in the projectionlight, each image can be observed from respective predetermineddirection. Furthermore, by setting observable direction of each image atan angle narrower than a space between the eyes of an observer, theobserver can view a stereoscopic image. Furthermore, in the imageprojection system including the projection type screen of the firstembodiment, a projector to obtain the projection light is only one usualprojector. Accordingly, scale of the system is miniaturized.

In the first embodiment, a section of each reflection surface along ahorizontal direction has a parabolic shape concave facing incidentdirection of projection light. A directrix of the parabola of eachreflection surface coincides, and the focus point of each parabolicreflection surface exists on the same straight line parallel to thedirectrix. If the projector 201 is sufficiently distant from theprojection type screen 101, projection light 1 incident to theprojection type screen 101 is almost parallel. Accordingly, if a pitchof neighboring reflection surfaces on the reflection surface array 102is equal to a pitch of divided images included in the projection light1, as shown in FIG. 11, images reflected by each reflection surface areparallel.

However, if a distance between the projector 201 and the projection typescreen 101 is short, projection light 1 incident to the projection typescreen 101 is not parallel. In this case, as shown in FIG. 12,projection light incident to the edge of the projection type screen 101is reflected along a direction toward the outside from the screen.

Accordingly, as shown in FIG. 13, a reflection surface of the reflectionsurface array 102 is formed having a parabolic shape concave toward theprojection light 1 so that each straight line perpendicular to adirectrix of each parabola and passing through a focus of the parabolacrosses at the same point in front of the screen and each focus existson the same straight line. In this case, a projection light incidentnear the edge of the reflection surface is prevented from beingreflected toward the outside of the reflection surface. Furthermore, aposition of an exit pupil of a projection lens of the projector islocated at a cross point of straight lines each perpendicular to thedirectrix of a parabola and passing through a focus point of theparabola. In this case, light reflected by each reflection surfacedirects toward the projector, and an observer neighboring the projectorcan effectively recognize a stereoscopic image. As a projection light 1including an image, the image may not be equally divided and arranged asshown in FIG. 5. In proportion to the angle of reflection of light fromeach reflection surface, the image may be divided at a wider interval ofdivision toward the edge of the image.

Furthermore, as shown in FIG. 14, the reflection surface array may beformed so that each straight line perpendicular to a directrix of aparabola of each reflection surface and passing through a focus point ofthe parabola crosses at the same point in front of the screen and thefocus points of each parabola exist on an arc of a circle centered atthe same point. In this case, a position of an exit pupil of aprojection lens is located at a cross point of straight lines eachperpendicular to a directrix of a parabola and passing through a focusof the parabola. Accordingly, a distance from the position of the exitpupil of the projection lens to each reflection surface coincides, andposition relationship between the exit pupil and the focus of eachreflection surface can be fixed.

Furthermore, as shown in FIG. 15, a reflection surface array in which asection of each reflection surface along a horizontal direction has aparabolic shape convex to an incident direction of the projection lightcan be used. In this case, each reflection surface is formed so thateach straight line perpendicular to a directrix of each parabola andpassing through a focus point of the parabola crosses at the same pointin front of the screen and each focus point exists on the same straightline. In this way, even if each reflection surface of the reflectionsurface array is convex to the incident direction of the projectionlight, by adjusting a projection position of the projection light oneach reflection surface, each image included in the projection light canbe viewed from a predetermined direction.

As mentioned-above, in the reflection surface 102, a section of eachreflection surface along a horizontal direction is convex to theincident direction of the projection light. On the other hand, in astereoscopic image display apparatus of direct view type,autostereoscopy is possible by observing a light outgoing from behind abarrier having a slot through pixels located in front of the barrier.FIGS. 16A and 16B show a relationship between the stereoscopic imagedisplay apparatus of direct view type and the reflection surface array102 of the first embodiment. In the stereoscopic image display apparatusof direct view type of FIG. 16A, a light is outgoing by backlight frombehind pixels 401 (opposite side of the observer) through a barrier 402having a slit. The light transmitted through the slit of the barrier 402is modulated by the pixels 401 and transformed as a display image inwhich each image (A, B, C) has a directivity along a predetermineddirection. Accordingly, the observer positioned in front of the pixels401 can view each image (A, B, C) from the predetermined direction.

On the other hand, in the reflection array 102 of the projection typescreen 101, as shown in FIG. 16B, an incident light to the reflectionsurface array 102 as parallel light is reflected along differentdirection based on the incident position. Accordingly, in the same wayas the concave section of the reflection surface, by coinciding a pitchof each reflection surface with a pitch of divided images included inthe projection light, each image (A, B, C) can be observed fromrespective predetermined direction.

Furthermore, in case that a shape of each reflection surface is aparabolic shape convex to the incident direction of projection light, asshown in FIG. 17, the reflection surface array can be formed so thateach straight line perpendicular to a directrix of a parabola of eachreflection surface and passing through a focus of the parabola crossesat the same point in front of the screen and a focus of each parabolaexists on a circle centered at the same point. In this case, a positionof an exit pupil of a projection lens is located at a cross point ofstraight lines each perpendicular to a directrix of a parabola andpassing through a focus of the parabola. Accordingly, a distance fromthe position of the exit pupil of the projection lens to each reflectionsurface coincides, and the position relationship between the exit pupiland the focus of each reflection surface can be fixed.

The Second Embodiment

In the first embodiment, a section of each reflection surface of thereflection surface array along a horizontal direction has a parabolicshape. However, in the second embodiment, a section of each reflectionsurface of the reflection surface array along a horizontal direction hasan elliptic shape.

FIGS. 18A and 18B respectively show a section of the projection typescreen 501 along a horizontal direction and a vertical directionaccording to the second embodiment. As shown in FIG. 18A, a section ofeach reflection surface of the reflection surface array 502 has anellipse shape concave to an incident direction of the projection light1. A lenticular sheet 503 is the same component as the projection typescreen 101 of the first embodiment. Accordingly, explanation of thelenticular sheet 503 is omitted.

FIG. 19 is a schematic diagram showing the relationship among eachreflection surface of the reflection surface array 502 of the projectiontype screen 501 according to the second embodiment. As shown in FIG. 19,each reflection surface has an elliptic shape concave to an incidentdirection of the projection light 1. An elliptic shape of eachreflection surface is formed so that a straight line perpendicular to adirectrix of each ellipse and passing through a focus of the ellipsecrosses a first focus distant from the reflection surface of the ellipseand a second focus near the reflection surface of the ellipse. Briefly,the first focus and the second focus exist on the same straight line.

In this way, even if each reflection surface of the reflection surfacearray 502 is an elliptic shape, a plurality of images included in theprojection light 1 are respectively reflected along different directionbased on an incident direction of the projection light 1 to eachreflection surface. Accordingly, in the same way as the firstembodiment, by coinciding a pitch between neighboring reflectionsurfaces of the reflection surface array 502 with a pitch of dividedimages included in the projection light 1, each image can be observedfrom a respective predetermined direction. Furthermore, by setting adirection from which each image is observable at an angle narrower thana space between the eyes of an observer, the observer can view astereoscopic image.

Next, as for each reflection surface of the reflection array 502 of theprojection type screen 501, the relationship among a focus distance L(projection distance) between the reflection surface and the first focuspoint, a focus distance g between the reflection surface and the secondfocus point, and a pitch D between neighboring reflection surfaces isexplained. Hereinafter, assume that a projection distance L issufficiently large, and the projection distance L is equal to the focusdistance g.

As shown in FIG. 20, a coordinate of a point P on a reflection surfaceis represented by polar-coordinate (ρ, φ) centered at the second focuspoint of the reflection surface. In this case, ρ represents a distancebetween the second focus point and the point P, and φ represents anangle between a straight line perpendicular to a directrix and passingthrough the second focus, and a straight line passing through the secondfocus and the point P. The relation among the focus distance g, theprojection distance L, and a distance ρ between the point P and thesecond focus, is represented as following equation (3).

$\begin{matrix}{{L = {{2c} + g}}{\rho = \frac{p}{1 + {{ \cdot \cos}\; \varphi}}}} & (3)\end{matrix}$

In this case, c represents a distance between a center of ellipse andeach focus. Furthermore, p and e respectively represent a focusparameter (½ of chord parallel to short axis and passing through thefocus) and an eccentricity of the ellipse. A long radius and a shortradius of the ellipse are respectively a and b. The focus parameter andthe eccentricity are represented as following equation (4).

$\begin{matrix}{{L = \frac{b^{2}}{a}}{e = {\frac{c}{a} = \frac{\sqrt{a^{2} - b^{2}}}{a}}}} & (4)\end{matrix}$

In this case, a maximum outgoing angle (φ in case that P is on the edgeof the reflection surface) of a reflection light is φ_(MAX), and ρ forthe maximum going angle is ρ_(MAX). A pitch D between neighboringreflection surfaces of the reflection surface array 502 is representedas following equation (5).

$\begin{matrix}{D = \frac{4{gL}}{{g \cdot \left( {1 - {\cos \; \varphi_{MAX}}} \right)} + {L \cdot \left( {1 + {\cos \; \varphi_{MAX}}} \right)}}} & (5)\end{matrix}$

The maximum outgoing angle φ_(MAX) of the reflection light is aparameter to describe observable area of a stereoscopic image. If theobservable area is previously set as φ_(MAX), the pitch D betweenneighboring reflection surfaces of the reflection surface array 502 iscalculated using the equation (5).

As mentioned-above, a shape of each reflection surface is fixed, and aprojector is located so that an exit pupil of the projector ispositioned at the first focus in FIG. 19. In this case, a reflectionlight from each reflection surface is directed toward the projector.Accordingly, an observer neighboring the projector can effectivelyrecognize a stereoscopic image.

In this way, in the projection type screen of the second embodiment,even if a section of each reflection surface of the reflection arrayalong a horizontal direction is an elliptic shape, the stereoscopicimage can be observed.

In the second embodiment, as for an ellipse of each reflection surfaceof the reflection surface array 502, the second focus points near thereflection surface exist on the same straight line. However, as shown inFIG. 21, the second focus point may exist on the same circle centeringthe first focus. In this case, the reflection surface array 502 has thesame shape of reflection surface at the center and the edge of a screen,and a projection distance from the projector to each reflection surfacecan coincide. Accordingly, by locating an exit pupil of the projector atthe first position in FIG. 21, the positional relationship between theexit pupil and the focus point of each reflection surface can be fixed.

Furthermore, as shown in FIG. 22, a reflection surface array in which asection of each reflection surface along a horizontal direction is anelliptic shape convex to an incident direction of the projection lightcan be used. In this case, each reflection surface is formed so thateach straight line perpendicular to a directrix of each ellipse andpassing through a focus point of the ellipse crosses at the same pointin front of the screen and each focus point exists on the same straightline. In this way, even if each reflection surface of the reflectionsurface array is a convex to the incident direction of the projectionlight, by adjusting a projection position of the projection light oneach reflection surface, each image included in the projection light canbe viewed from a predetermined direction.

Furthermore, in case that a shape of each reflection surface is anelliptic shape convex to the incident direction of projection light, asshown in FIG. 23, the reflection surface array can be formed so thateach straight line perpendicular to a directrix of an ellipse of eachreflection surface and passing through a focus point of the ellipsecrosses at the same point in front of the screen and the focus of eachellipse exists on a circle centered at the same point. In this case, thereflection surface array has the same shape of reflection surface forthe center and the edge of a screen. Furthermore, a position of an exitpupil of a projection lens is located at a cross point of straight lineseach perpendicular to a directrix of an ellipse and passing through afocus point of the ellipse. Accordingly, a distance from the position ofthe exit pupil of the projection lens to each reflection surfacecoincides, and the positional relationship between the exit pupil andthe focus of each reflection surface can be fixed.

The Third Embodiment

In the third embodiment, an element for selecting between transmissionand scattering states is located between the reflection surface arrayand the lenticular sheet. By switching state of the element, display ofstereoscopic image and display of usual display can be selected in theprojection type screen.

FIGS. 24 A and B are respectively sections of the projection type screen601 along a horizontal direction and a vertical direction according tothe third embodiment. As shown in FIGS. 24 A and B, the projection typescreen 601 has a reflection array 602, an element 603 for selectingtransmission and scattering states, a lenticular sheet 604, and aswitching unit 605. In the reflection surface array 602, a plurality ofreflection surfaces having a mirror reflectivity each of which sectionalong a horizontal direction is a parabolic shape are arranged along thehorizontal direction. The element 603 for selecting transmission andscattering states is located at an incident side of a projection lightfor the reflection array 602. The lenticular sheet 604 havingdiffusivity along a vertical direction is located at the incident sideof the projection light for the element 603. The switching unit 605switches between transmission and scattering states of the element 603by applying a voltage to the element 603.

In comparison with the first embodiment, the element 603, of whichtransmission and scattering states are switched, is located between thereflection surface array 602 and the lenticular sheet 604. Thereflection surface array 602 and the lenticular sheet 604 are the sameas in the first embodiment.

By applying a voltage from the switching unit 605, the element 603 canswitch between transmission and scattering states. In case of displayinga stereoscopic image by a projection light 1 from the projector, theswitching unit 605 applies a voltage to the element 603, and the element603 is under a transmission state. In this case, an incident light tothe element 603 is incident to the reflection surface array 602 withoutscattering. Accordingly, in the same way as in the first embodiment,each division image included in the incident light 1 is reflected alonga respective predetermined direction by the reflection surface array602, and the observer can view a stereoscopic image.

On the other hand, in case of displaying a usual image, the switchingunit 605 does not apply a voltage to the element 603. In this case, theelement 603 is under a scattering state. Accordingly, as shown in FIG.25, when a projection light 1 transmits through the element 603, theprojection light 1 is scattered along arbitrary directions. Briefly,mirror reflectivity of the reflection surface array 602 is concealed,and reflection of projection light 1 by the projection type screen 601is set as scattering reflection.

By selecting transmission state and scattering state in the element 603using the switching unit 605, for example, in case of projecting a usualtwo-dimensional image from a projector, the element 603 is set asscattering state, and the projection type screen 601 functions as ausual screen. In case of displaying a stereoscopic image, the element603 is set as transmission state by the switching unit 605, and theprojection type screen 601 functions in order for the observer to view astereoscopic image.

As the element 603 of selecting transmission and scattering state, bymixing a monomer with a liquid crystal molecule and sealing into a cell,a liquid crystal element polymerized by UV irradiation can be used. Forexample, Polymer Dispersed Liquid Crystal (PDLC) elements or PolymerNetworked Liquid Crystal (PNLC) elements can be used.

Furthermore, by applying a voltage to only a part of the element 603using the switching unit 605, a part of the element 603 can be set astransmission state and another part of the element 605 can be set asscattering state. In this case, an image including both a usualtwo-dimensional image and a stereoscopic image can be observed on theprojection type screen 601. In order to apply voltage to only a part ofthe element 603, for example, a transparent electrode is divided,connected with the element 603, and driven by segment.

In this way, in the projection type screen of the third embodiment, theelement for selecting between transmission and scattering states islocated between the reflection surface array and the lenticular sheet.Accordingly, based on a projection image from the projector, astereoscopic image and a usual two-dimensional image can be selectivelyobserved.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

1.-20. (canceled)
 21. A projection type screen, comprising: a reflection surface array including a plurality of reflection surfaces along a horizontal direction, each reflection surface having a quadratic curve shape along the horizontal direction; a lenticular sheet at an incident side of a projection light for the reflection surface array, the lenticular sheet having a diffusivity along a vertical direction; and an element for selecting between transmission state and scattering state, the element being located between the reflection surface array and the lenticular sheet.
 22. The projection type screen according to claim 21, further comprising: a switching unit that switches between transmission state and scattering state of the element by applying a voltage to the element.
 23. An image projection system, comprising: a light emitting apparatus emitting a projection light including a display image; and a projection type screen on which the projection light is incident; said projection type screen comprising a reflection surface array including a plurality of reflection surfaces along a horizontal direction, each reflection surface having a quadratic curve shape along the horizontal direction; a lenticular sheet at an incident side of a projection light for the reflection surface array, the lenticular sheet having diffusivity along a vertical direction; and an element for selecting between transmission state and scattering state, the element being located between the reflection surface array and the lenticular sheet.
 24. The projection type screen according to claim 23, further comprising: a switching unit that switches between transmission state and scattering state of the element by applying a voltage to the element. 